From the Guidelines
For a patient presenting with myalgias, I recommend ordering a comprehensive panel of laboratory tests to identify potential causes, including complete blood count (CBC), comprehensive metabolic panel (CMP), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), creatine kinase (CK), and thyroid-stimulating hormone (TSH), as suggested by the most recent guidelines 1. When evaluating a patient with myalgias, it is essential to consider various potential causes, including inflammatory, metabolic, endocrine, infectious, and medication-induced conditions.
- Initial testing should include:
- Complete blood count (CBC) to rule out infections or hematological disorders
- Comprehensive metabolic panel (CMP) to assess electrolyte and renal function
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to evaluate inflammatory markers
- Creatine kinase (CK) to assess muscle damage
- Thyroid-stimulating hormone (TSH) to evaluate thyroid function
- Additional tests to consider based on clinical suspicion include:
- Aldolase
- Antinuclear antibody (ANA)
- Rheumatoid factor (RF)
- Vitamin D level
- HMG-CoA reductase antibody if statin use is present
- In cases with specific risk factors, consider testing for infectious causes such as viral studies (including HIV, hepatitis), Lyme disease serology, or trichinosis antibodies
- Electromyography and muscle biopsy may be necessary if inflammatory myopathies are suspected, as suggested by 1 and 1 These tests help distinguish between various causes of muscle pain and guide further diagnostic workup and treatment decisions.
- CK elevation suggests muscle damage, while inflammatory markers like ESR and CRP help identify inflammatory conditions
- Thyroid function tests are important as both hypothyroidism and hyperthyroidism can cause myalgias
- Vitamin D deficiency is a common reversible cause of muscle pain that should not be overlooked, as noted in the guidelines 1
From the Research
Laboratory Tests for Myalgias
To diagnose the underlying cause of myalgias, several laboratory tests can be ordered. These tests include:
- Creatine kinase (CK) levels: Elevated CK levels can indicate muscle damage or myopathy 2, 3, 4
- Thyroid function tests: Thyroid disease can cause myalgias, and thyroid function tests can help diagnose this condition 2
- (25)OH vitamin D levels: Osteomalacia, a condition caused by vitamin D deficiency, can cause myalgias, and measuring vitamin D levels can help diagnose this condition 2
- Electromyography (EMG): EMG can help diagnose muscle disorders, such as myopathy or muscular dystrophy 3
- Ultrasound: Muscle ultrasound can help diagnose muscle disorders, such as myopathy or muscular dystrophy 3
- Muscle biopsy: A muscle biopsy can help diagnose muscle disorders, such as myopathy or muscular dystrophy 2, 3
- Complete blood count (CBC): While not specific for myalgias, a CBC can help diagnose underlying conditions, such as infections or inflammation, that may be causing myalgias 5, 6
- Liver function tests (LFTs): LFTs can help diagnose underlying conditions, such as liver disease, that may be causing myalgias 4, 5
Special Considerations
In certain cases, additional laboratory tests may be necessary, such as:
- Anti-Jo1 antibody testing: This test can help diagnose inflammatory myopathies, such as dermatomyositis or polymyositis 2
- Malignancy screening: In some cases, myalgias can be a symptom of an underlying malignancy, and screening tests, such as imaging studies or tumor markers, may be necessary 2, 5
- Immune checkpoint inhibitor-related myositis testing: In patients who have received immune checkpoint inhibitors, such as nivolumab or ipilimumab, testing for myositis may be necessary 4